Methods for heating various finely divided materials are widely used in the industry. While many heating mediums may be used steam is generally preferred. In many processes involving food material, the starting material is heated indirectly to avoid heat damaging of the material, risk of contamination, and addition of water to the final product.
As an example of a closed circuit design using indirect heating is disclosed in U.S. Pat. No. 4,653,198 (Stord Bartz). The document describes a plant for two-stage heat treatment of animal or vegetable material. A heating medium which is used in a second heat treatment apparatus, which follows the first heat treatment apparatus, consist of a uncontaminated water/steam stream which is circulated in a closed circuit, that is to say separated from the heat medium of the first apparatus and from the treatment material of the second apparatus.
Direct injection of steam to the starting material offers a more efficient and faster heating due to the absent of heat exchanger surfaces to transfer the heat from the heating medium to the material being processed. EP 671 129 (Finnatec) describes a process and an apparatus for treatment of products in the food industry. In the known process steam is directly injected into a food material being processed. The water used for generating the steam has prior to the evaporation process been heated in countercurrent with the steam-heated food material. Furthermore, the water used for steam-generation has been removed in a preceding step, such as a step involving ultrafiltration, reverse osmosis, nanofiltration, and evaporation.
It is the purpose of the present invention to device a process and a plant that improves direct steam injection technology. While the direct injection of the steam into a material being processed result in a quicker heating process it also adds considerable amounts of condensed water to the product stream. The additional water dilutes the final product. The present invention suggests a method for extracting the additional water from the diluted product.